This invention relates to a magnetic resonance imaging apparatus (referred to hereafter as MRI), and in particular to a magnetic resonance imaging apparatus which performs imaging by assigning magnetic tags, and a magnetic resonance imaging method.
The terminology used in the following description of this specification is summarized below.
[Tagging Sequence]: Sequence for applying magnetic field which performs magnetic tagging (pulse sequence).
[Imaging Sequence]: Sequence for applying magnetic field which performs magnetic resonance imaging (MRI) (pulse sequence).
[Amplitude Modulated Burst Pulse]: Radiofrequency burst pulse comprising plural sub-pulses formed at equal intervals on the time axis whereof the amplitudes are modulated by a sinc function (the plural sub-pulses comprise a sub-pulse of amplitude value 0).
[Period in Cardiac Cycle]: The times when one cardiac cycle is divided into for example, approximately, 4-12 parts when extracting the amount of movement of the heart wall.
[Echo Signal Gathering Efficiency]: Number of echo signals gathered in unit time.
First, the prior art technology will be described regarding analysis of cardiac function by performing magnetic tagging to image the motion of the heart wall (Ref. 1: L. Axel et al., MR Imaging of Motion with Spatial Modulation of Magnetization: Radiology, vol. 171, p. 841-845 (1989)).
FIG. 17 is a diagram describing the principle of assigning magnetic tags disclosed in Ref. 1. FIG. 17A is a diagram describing a tagging sequence. FIG. 17B is a diagram describing the behavior of magnetization vectors in the tagging sequence of FIG. 17A, and FIG. 17C is a diagram describing the spatial intensity distribution of the z direction component of the nuclear magnetization vector.
In FIG. 17, a static magnetic field is applied in the z direction. As shown in FIG. 17B, in the initial state (time 0) shown in FIG. 17A, the nuclear magnetization vector is oriented in the z direction, and as shown in FIG. 17C, the intensity of the z direction component of the nuclear magnetization vector is M0 (constant value). As shown in FIG. 17A, when a radiofrequency magnetic field pulse RF is irradiated at a time a, the nuclear magnetization vector rotates around the x axis and inclines at an angle xcex8 in the yz plane, and the intensity of the z direction component of the nuclear magnetization vector is M0 cos xcex8. Next, as shown in FIG. 17A, when a gradient magnetic field Gx is applied at a time b, the nuclear magnetization vector is phase-modulated corresponding to the position coordinates.
FIG. 18 is a diagram describing the intensity of the x direction component of the nuclear magnetization vector in a tagging sequence according to the prior art. As shown in FIG. 18, the intensity of the x direction component of the nuclear magnetization vector after applying the inclined magnetic field Gx is modulated relative to the x direction in which the gradient magnetic field Gx is applied. However, as shown in FIG. 17C, the intensity of the z direction component of the nuclear magnetization vector is M0 cos xcex8 (constant value). The nuclear magnetization vector precesses around the z axis.
Subsequently, as shown in FIG. 17A, when the radiofrequency magnetic field pulse RF is again irradiated at a time c, the nuclear magnetization vector rotates around the x axis, and inclines at an angle xcex8 in the yz plane. As a result, the modulation in the x direction of the nuclear magnetization vector shown in FIG. 18 is reflected in the z direction component of the nuclear magnetization vector. Due to the tagging sequence described above, as shown in FIG. 17C, at a time d before the imaging sequence is implemented, the z direction component of the nuclear magnetization vector can be modulated corresponding to the x coordinate.
When the imaging sequence is implemented, the above spatial modulation of the z direction component of the nuclear magnetization vector is reflected in the signal intensity of the acquired image, and stripes are generated perpendicular to the x direction on the image. Specifically, magnetization is suppressed in the peripheral part of the stripes on the image obtained by the tagging sequence shown in FIG. 17A. By a combination of the applied amount and applied direction of the gradient magnetic field, the direction of the stripes and interval of the stripes can be controlled, and stripes can also be generated in the vertical and horizontal directions. These stripes are tags.
FIG. 19 is a diagram describing the tagging sequence in the prior art. In FIG. 17, the simplest example has been shown to describe the principle of tagging, but in general, a binomial SPAMM (Spatial Modulation of Magnetization) pulse which makes the amplitude ratio of the radiofrequency magnetic field pulses RF3xe2x80x2, 5xe2x80x2 a binomial coefficient is often used (Ref. 2: L. Axel, et al., Heart Wall Motion: Improved Method of Spatial Modulation of Magnetization for MR Imaging, Radiology, vol. 172, p. 349-350 (1989)), as shown in FIG. 19. The numbers above the radiofrequency magnetic field pulse RF shown in FIG. 19 are amplitude ratios of radiofrequency magnetic field pulses.
In the example shown in FIG. 19, a gradient magnetic field Gx4xe2x80x2 in the x direction is applied alternately with a radiofrequency magnetic field pulse RF3xe2x80x2, a gradient magnetic field Gx6xe2x80x2 in the y direction is applied alternately with a radiofrequency magnetic field pulse RF5xe2x80x2, and tags are assigned in the x direction and y direction. As described hereabove, if the method disclosed in Ref. 1 is used, the nuclear magnetization is suppressed at equal intervals in straight lines in the vertical and horizontal directions, i.e. in a grid shape. As a result, if the imaging sequence is implemented immediately after completion of the tagging sequence, an MRI image is obtained having bright points arranged in a lattice.
In general, a pulse sequence according to a fast imaging method is used as the imaging sequence, particularly the pulse sequence in the fast spin echo technique (Ref. 3: D. Matthaei et al., Cardiac and Vascular Imaging with an MR Snapshot Technique, Radiology, vol. 177, pp. 527-532 (1990)). The fast spin echo technique is suitable for extraction of the heart wall. It may be mentioned that the echo planar (EPI) technique is suited to extraction of blood circulation, but not to extraction of the heart wall.
FIG. 25 is a diagram describing the imaging sequence in the prior art. FIG. 25A is fast spin echo type pulse sequence wherein a radiofrequency burst pulse, comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function, is applied. FIG. 25B shows a pulse sequence according to the fast spin echo method.
In the pulse sequence shown in FIG. 25A, after a first amplitude modulated burst pulse is irradiated, a slice gradient magnetic field Gs is applied, a xcfx80 pulse is irradiated, and slice selection and inversion of magnetization are performed. Next, a readout gradient magnetic field Gr is applied, the phase of the nuclear magnetization is provided to generate an echo signal, and the echo signal is measured. Subsequently, inversion of magnetization due to irradiation by the xcfx80 pulse and application of the readout gradient magnetic field following the xcfx80 pulse are repeated to generate echo signals on plural occasions, and measurement of the echo signal is repeated. The number of echo signals generated by one irradiation with the xcfx80 pulse is equal to the number of sub-pulses in the first amplitude modulated burst pulse. It should be noted that different phase encodings are assigned to the echo signals by a phase encoding gradient magnetic field Gp.
In the pulse sequence (imaging sequence) shown in FIG. 25A, after a second amplitude modulated burst pulse is irradiated wherein the carrier frequency of the first amplitude modulated burst pulse is shifted, a xcfx80 pulse is irradiated and the echo signal is measured in the same way as following the first amplitude modulated burst pulse. In the example shown in FIG. 25A, five echo signals are generated for each irradiation of a xcfx80 pulse. However, only the most important echo signals may be gathered considering the SN ratio and echo signal measuring time.
In the pulse sequence shown in FIG. 25B, the slice gradient magnetic field Gs is applied, a xcfx80/2 pulse is irradiated, a slice is selected, and the readout gradient magnetic field Gr is applied to disperse the phase of the nuclear magnetization. Next, the slice gradient magnetic field Gs is applied, the xcfx80 pulse is irradiated to invert the nuclear magnetization, the readout gradient magnetic field Gr is applied, the phase of the nuclear magnetization is provided to generate an echo signal, and the echo signal is measured.
Subsequently, the slice gradient magnetic field Gs is applied, inversion of nuclear magnetization with irradiation of the xcfx80 pulse and application of the readout gradient magnetic field are repeated, an echo signal is generated on plural occasions, and measurement of the echo signal is repeated. It should be noted that different phase encodings are assigned to the echo signals by the phase encoding gradient magnetic field Gp.
FIG. 20 is a diagram describing the pulse sequence in a prior art MRI apparatus wherein tagging is performed and the motion of the heart wall is imaged. Hereafter, the method of detecting the motion of the heart wall will be described using FIG. 20. Information regarding the motion of the heart wall is obtained by modifying the start time of an imaging sequence 40. For example, a synchronizing signal 2 is output at which an R wave 1 of an electrocardiogram is maximized, a tagging sequence 30 is performed at a time t0 immediately after input of the synchronizing signal, and the imaging sequence 40 is begun at a time t1. Next, the tagging sequence 30 is implemented at the time t0 immediately after the synchronizing signal 2 detected from the R wave of the electrocardiogram, and the MRI image is acquired by modifying only the start time of the imaging sequence 40, i.e., t1, t2, t3 . . .
Herein, if for example the MRI image 1 obtained if the imaging sequence is started at the time t1 and the MRI image 2 obtained if the imaging sequence is started at the time t2 are compared, the positions of the bright spots on the image vary. The displacement amount of the bright spots of the tags reflects the displacement amount of the heart wall from the time t1 to the time t2. Using plural MRI images obtained by modifying the start time of the imaging sequence, i.e., t1, t2, t3 . . . the amount of movement of the heart wall and the speed of motion of the heart wall, which are important parameters in evaluating cardiac function, can be extracted.
In the prior art for imaging the movement of the heart using tags, there are two problems. The bright spots of the tags are obtained by suppressing the signal at the periphery, so the larger the time interval from completion of the tagging sequence to start of the imaging sequence, the better the recovery of the suppressed nuclear magnetization. In general, the recovery time is longer in the case the magnetization is suppressed more strongly. At the time d shown in FIG. 17C, the larger the intensity difference between the broken line representing signal intensity prior to modulation and the solid line representing signal intensity after modulation, the longer the recovery time required. Here, it is seen that if bright spots are represented by the area of the signal intensity M0, the nuclear magnetization recovers in a short time in its vicinity. In other words, the larger the time interval up to start of the imaging sequence, the larger the size of the bright spots due to recovery of nuclear magnetization. This is the phenomenon referred to as blurring of the bright spots. If the bright spots are blurred, identification of the bright spots of the tags is difficult, and the precision involved in extracting the amount of movement of the heart wall declines.
To extract the amount of movement of the heart wall, an MRI image is generated in each period of the cardiac cycle. If a new dimension, i.e. the period of the cardiac cycle, is added to the number of dimensions of an ordinary MRI image (e.g., 2 dimensions for a flat image), the subject has to be restrained for a long time. For example, the imaging time for one slice in the prior art imaging technique is 32 seconds. If there are 12 slices and the period of the cardiac cycle is divided into 12 parts, the subject must be restrained for at least 70 minutes to acquire an image, and this is stressful for the subject.
A technique was therefore desired to resolve the above problems and extract the cardiac function to high precision in a short time.
It is therefore an object of this invention to provide a magnetic resonance imaging apparatus which can apply an amplitude modulated burst pulse and gradient magnetic field in a predetermined sequence, modify nuclear magnetization vectors corresponding to positional coordinates to assign tags, acquire an MRI image, and extract a cardiac function to high precision in a short time.
According to this invention, an amplitude modulated burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function ({sin(t)}/t), is used as an excitation radio frequency magnetic field pulse for a tagging sequence which performs tagging, and an imaging sequence which performs imaging of a magnetic resonance image. According to this invention, tags where blurring of bright spots is small can be assigned in at least one direction, and imaging can be performed in a short time. Also, according to this invention, a cardiac function analysis can for example be performed which quantitatively evaluates the pump function of the heart by detecting the motion of the heart wall. Hereafter, the representative features of the invention will be described.
The nuclear magnetic resonance imaging apparatus of this invention comprises a static magnetic field generating means in which a subject to be inspected is placed, a gradient magnetic field of generating means which generates a gradient magnetic field in three (first, second and third) perpendicular directions, a radiofrequency magnetic field generating means which generates a radiofrequency magnetic field, a signal detecting means which detects a nuclear magnetic resonance signal generated from the subject to be inspected, and a physiological signal detecting means which detects a periodic physiological signal from the subject to be inspected. It further comprises a control means which controls the gradient magnetic field generating means, radiofrequency magnetic field generating means, signal detecting means and physiological signal detecting means, and performs control to implement a predetermined pulse sequence.
The control means (1) detects a physiological signal based on respiration or heartbeat, etc., and generates a synchronizing signal which initiates a pulse sequence which detects a nuclear magnetic resonance signal (echo signal) from the physiological signal.
In a first construction of the nuclear magnetic resonance apparatus of this invention, the control means further (2) synchronizes a first radiofrequency burst pulse (first amplitude modulated burst pulse) comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in one direction (first or second direction) of the three directions with the synchronizing signal, applies them, modulates the nuclear magnetization of the subject to be inspected in one direction, and controls the tagging sequence in one direction.
In a second construction of the nuclear magnetic resonance apparatus of this invention, the control means further (2) synchronizes the first radiofrequency burst pulse (first amplitude modulated burst pulse) comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in the first direction, applies them, modulates the nuclear magnetization of the subject to be inspected in the first direction, and (3) applies a second radiofrequency burst pulse (second amplitude modulated burst pulse) comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in the second direction, modulates the nuclear magnetization of the subject to be inspected in the second direction, and controls the tagging sequence in the first and second directions.
In the aforesaid first and second constructions, the nuclear magnetization of the subject in a rectangular periodic region is excited, so compared to modulation of nuclear magnetization by a trigonometric function in the tagging of the prior art, tags with much less blurring of bright spots can be assigned. As a result, the movement and thickness deformations of the heart wall and valves in one or two dimensions can be measured to high precision from the image reconstructed from the echo signals measured by the imaging sequence performed after the tagging sequence.
In a third construction of the nuclear magnetic resonance imaging apparatus of this invention, in addition to (1) and (2) of the first construction, the control means (3) applies the second radiofrequency burst pulse (second amplitude modulated burst pulse) comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in the first direction to excite the nuclear magnetization of the subject to be inspected after a predetermined waiting time has elapsed following implementation of (2), (4) applies a radiofrequency magnetic field pulse while a gradient magnetic field is applied in the third direction, (5) assigns positional information in the second direction to the nuclear magnetization due to application of the gradient magnetic field in the second direction, generates a nuclear magnetic resonance signal in which positional information in the first direction is assigned to the nuclear magnetization due to application of the gradient magnetic field in the first direction, and measures the nuclear magnetic resonance signal, (6) repeats the steps (4) and (5) plural times, and (7) repeats the steps from (1) to (6) plural times. Further, in the third construction, images of the heart are reconstructed in the same period of the cardiac cycle or different periods of the cardiac cycle by performing (7) where the aforesaid predetermined waiting time is constant, and by varying the predetermined waiting time on each occasion the steps (1) to (6) in (7) are repeated.
In a fourth construction of the nuclear magnetic resonance imaging apparatus of this invention, in addition to (1), (2) and (3) of the second construction, the control means (4) applies a third radiofrequency burst pulse (third amplitude modulated burst pulse) comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in the first direction to excite the nuclear magnetization of the subject to be inspected after a predetermined waiting time has elapsed following implementation of (3), (5) applies a radiofrequency magnetic field pulse while a gradient magnetic field is applied in the third direction, (6) assigns positional information in the second direction to the nuclear magnetization due to application of the gradient magnetic field in the second direction, generates a nuclear magnetic resonance signal in which positional information in the first direction is assigned to the nuclear magnetization due to application of the gradient magnetic field in the first direction, and measures the nuclear magnetic resonance signal, (7) repeats the steps (5) and (6) plural times, and (8) repeats the steps from (1) to (7) plural times. Further, in the fourth construction, images of the heart are reconstructed in the same period of the cardiac cycle or different periods of the cardiac cycle by performing (8) where the aforesaid predetermined waiting time is constant, and by varying the predetermined waiting time on each occasion the steps (1) to (7) in (8) are repeated.
In the aforesaid third and fourth constructions, the nuclear magnetization of the subject in a rectangular periodic region is excited, the width of the rectangular periodic region is larger than the size of the pixels of the image reconstructed from the measured echo signal, the width of the rectangular periodic region is an integral number of times the size of the pixels of the reconstructed image, and the edge of the rectangular periodic region coincides with the boundary line between pixels of the reconstructed image. Therefore, compared to modulation of the nuclear magnetization by a trigonometric function with tags of the prior art, tags with much less blurring of bright spots can be assigned, and the image can be acquired in a short time. As a result, the movement and thickness deformations of the heart wall and valves in one or two dimensions can be measured to high precision from the reconstructed image, and useful information regarding heart disease can be obtained.
According to the aforesaid third and fourth constructions, the second and third amplitude modulated burst pulses are irradiated to perform fast image acquisition. In this invention, an imaging sequence is performed which excites nuclear magnetization at n (in general, n is the number of exponentiations of 2) frequencies, and an echo signal can be detected when the nuclear magnetization in the imaging cross-section containing the subject to be inspected is excited in a substantially uniform manner (Ref 4: U.S. Pat. No. 5,789,922).
The characteristic feature of this invention is that a radiofrequency burst pulse (amplitude modulated burst pulse) comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function, is applied with a pulse sequence which is at least one of a tagging sequence and an imaging sequence.
The application of this amplitude modulated burst pulse will now be summarized.
FIG. 22 is a diagram describing an amplitude modulated burst pulse of the prior art. The amplitude modulated burst pulse comprises plural sub-pulses whereof the amplitudes are modulated by a sinc function (period T), and the shape of the sub-pulses is a sinc function. Including the sub-pulse for which the amplitude value is 0, the interval between sub-pulses on the time axis is xcfx84.
FIG. 23 is a diagram describing the relation between impulse sequences in a real space and in a frequency space. A series of impulses (xcex4 function series 1) having a fixed interval xcfx84 on the time axis of real space and a series of impulses (xcex4 function series 2) having a fixed interval (1/xcfx84) on the frequency axis of frequency space, are related by a Fourier transformation.
In general, in imaging where a radiofrequency burst pulse is applied, the principle is used where an impulse having a fixed interval on the time axis is a spectra having a fixed interval on the frequency axis. If we consider the series of impulses (xcex4 function series 1) on the time axis shown in FIG. 23 as sub-pulses of a radiofrequency burst pulse, and a spectrum on the frequency axis (xcex4 function series 2) is an area where nuclear magnetization is excited, the correspondence relationship between the radiofrequency burst pulse and the excitation area can easily be understood.
To assign tags with less blurring of bright spots due to recovery of suppressed nuclear magnetization from the end of the tagging sequence to the start of the imaging sequence, it is desirable to completely suppress the nuclear magnetization of the area excepting the bright spots. The shape of the excitation area depends on the shape of the sub-pulses, and sub-pulses which make the shape of the excitation are a rectangular may be used.
FIG. 24 is a diagram describing the relation of the amplitude modulated burst pulse shown in FIG. 22 in real space and frequency space, and the correspondence relation between excitation frequency and the excitation area when an amplitude modulated burst pulse using two excitation frequencies is applied. By a Fourier transformation, the amplitude modulated burst pulse in real space shown in FIG. 22 becomes the rectangular periodic wave 1 having a specific width (xc2xd(2xcfx84)) on the frequency axis of the frequency space. The rectangular parts above the frequency axis of the waveform of the rectangular periodic wave 1 (comb-shaped area where rectangular parts for which the value on the vertical axis is not 0 are like the teeth of a comb) are areas excited by the amplitude modulated burst pulse.
If the relation between the time interval of the sub-pulses and the period T of the sinc function is T=2xcfx84, the areas which are excited and the areas which are not excited appear alternately with the same volume. On the frequency axis of the frequency space, the area where nuclear magnetization is excited is a rectangular periodic wave having a specific width, so in the tagging sequence using an amplitude modulated burst pulse, an ideal modulation of nuclear magnetization for assigning tags with less blurring of bright spots can be performed.
If the carrier frequency of the amplitude modulated burst pulse is shifted by 1/(2xcfx84) Hz, it becomes a rectangular periodic wave 2 wherein the rectangular periodic wave 1 is shifted by 1/(2xcfx84) Hz on the frequency axis. As a result, areas where the waveform of the rectangular periodic wave 1 is excited, are areas where the waveform of the rectangular periodic wave 2 is not excited, and areas where the waveform of the rectangular periodic wave 1 is not excited, are areas where the waveform of the rectangular periodic wave 2 is excited. In other words, the areas which are excited and the areas which are not excited are reversed in the rectangular periodic wave 1 and the rectangular periodic wave 2. Due to the irradiation of the subject to be inspected with these amplitude modulated burst pulses, the nuclear magnetization in the imaging cross-section of the subject to be inspected is substantially uniform.
Next, the imaging time required until measurement of the echo signal needed for image reconstruction is completed, and the imaging sequence, will be described. The imaging times due to the pulse sequences in FIG. 25A and FIG. 25B will be compared. If the data amount (e.g., number of sampling points acquired from one echo signal) is equal, the imaging times may be compared as indicators of the echo acquisition efficiency.
In FIG. 25A and FIG. 25B, the application times of the xcfx80 pulse, slice gradient magnetic field Gs and phase encoded gradient magnetic field Gp are identical. Therefore, the application time of the readout gradient magnetic field Gr and the number of echo signals generated during application of the readout gradient magnetic field Gr are the main factors in determining the echo acquisition efficiency.
In the pulse sequence of FIG. 25A, plural echo signals are generated corresponding to the number of sub-pulses in the first and second amplitude modulated burst pulses. In the pulse sequence of FIG. 25B, only one echo signal is generated due to application of one xcfx80 pulse. In the pulse sequence of FIG. 25A, the echo acquisition efficiency is several times that of the pulse sequence of FIG. 25B. Therefore, in the pulse sequence of FIG. 25A, the time for which the subject must be restricted to draw the heart can be shortened to a fraction compared to the pulse sequence of FIG. 25B. As the effect of movement of the subject is less, the reliability of the data is improved.
As described above, an amplitude modulated burst pulse is used in the tagging sequence and imaging sequence, so fast imaging can be performed, and higher precision of extracting cardiac functions is realized.
According to this invention, tags are assigned by applying an amplitude modulated burst pulse. This permits a large reduction in blurring of the bright spots of the tags, a large reduction in the time for which the subject must be restrained to acquire an image, fast imaging of the heart, and improved precision in extracting cardiac function.
The method of nuclear magnetic resonance imaging according to this invention has the following features.
First construction: (1) a step which detects a periodic physiological signal, (2) a step which generates a synchronizing signal which initiates a pulse sequence which detects, from the physiological signal, a nuclear magnetic resonance signal from a subject to be inspected, and (3) a step which synchronizes a first radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and a gradient magnetic field in a first or second direction with the synchronizing signal, applies them, and modulates the nuclear magnetization of the subject to be inspected in the first or second direction.
Second construction: (1) a step which detects a periodic physiological signal, (2) a step which generates a synchronizing signal which initiates a pulse sequence which detects, from the physiological signal, a nuclear magnetic resonance signal from a subject to be inspected, (3) a step which synchronizes a first radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and a gradient magnetic field in a first or second direction with the synchronizing signal, applies them, and modulates the nuclear magnetization of the subject to be inspected in the first direction, and (4) a step which applies a second radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function, and a gradient magnetic field, and modulates the nuclear magnetization of the subject to be inspected in the second direction.
Third construction: (1) a step which detects a periodic physiological signal, (2) a step which generates a synchronizing signal which initiates a pulse sequence which detects, from the physiological signal, a nuclear magnetic resonance signal, (3) a step which synchronizes a first radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and a gradient magnetic field in a first or second direction with the synchronizing signal, applies them, and modulates the nuclear magnetization of the subject to be inspected in the first or second direction, (4) applies the second radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in the first direction to excite the nuclear magnetization of the subject to be inspected after a predetermined waiting time has elapsed following implementation of the step (3), (5) applies a radiofrequency magnetic field pulse while a gradient magnetic field is applied in the third direction, (6) assigns positional information in the second direction to the nuclear magnetization due to application of the gradient magnetic field in the second direction, generates a nuclear magnetic resonance signal in which positional information in the first direction is assigned to the nuclear magnetization due to application of the gradient magnetic field in the first direction, and measures the nuclear magnetic resonance signal, (7) repeats the steps (5) and (6) plural times, and (8) repeats the steps from (1) to (7) plural times.
Fourth construction: (1) a step which detects a periodic physiological signal, (2) a step which generates a synchronizing signal which initiates a pulse sequence which detects, from the physiological signal, a nuclear magnetic resonance signal, (3) a step which synchronizes a first radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and a gradient magnetic field in a first direction with the synchronizing signal, applies them, and modulates the nuclear magnetization of the subject to be inspected in the first direction, (4) applies the second radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in the second direction to modulate the nuclear magnetization of the subject to be inspected in the second direction, (5) applies a third radiofrequency burst pulse comprising plural sub-pulses formed at equidistant intervals on the time axis whereof the amplitudes are modulated by a sinc function and the gradient magnetic field in the first direction to excite the nuclear magnetization of the subject to be inspected after a predetermined waiting time has elapsed following implementation of the step (4), (6) applies a radiofrequency magnetic field pulse while a gradient magnetic field is applied in the third direction, (7) assigns positional information in the second direction to the nuclear magnetization due to application of the gradient magnetic field in the second direction, generates a nuclear magnetic resonance signal in which positional information in the first direction is assigned to the nuclear magnetization due to application of the gradient magnetic field in the first direction, and measures the nuclear magnetic resonance signal, (8) repeats the steps (6) and (7) plural times, and (9) repeats the steps from (1) to (8) plural times.